Frog_Botherer

Hey all, new to the forum so thanks for your patience. I have a 1994 4Runner with the 3.0 V6, RWD, and an automatic transmission. It's mostly stock (which is fine by me) and it's got just over 200,000 miles on the odometer and an engine that was rebuilt about 10,000 miles ago. It's been a great truck, I absolutely love it, but recently I've been experiencing some transmission problems and I'd like your advice.

I'll try to lay out all the information I can. I'm not very good with cars (though I'm learning) and I suspect that I've already made a couple of (hopefully non-serious, easily-corrected) mistakes that might be contributing to my problem. I can follow instructions, but when left on my own I am not exactly the most useful person as far as cars and trucks are concerned.

So the first thing that I noticed was that every once in a while, when I first started the truck, the engine wouldn't idle quite right. It would sort of pulse up and down a bit like the idle speed wasn't quite enough to keep the engine going, and once or twice it actually did stall out. Shifting into gear and driving even a tiny bit would fix this – I wouldn't have to get the engine warmed up, just driving the car a few feet down the road would get it back to normal. This went on for a couple of weeks, and I had a mental note to take it in to a mechanic as soon as I could manage.

Now though, things are a bit weirder. Starting a few days ago, the car no longer had a low idle. Instead it had a high idle, but only in Park and Neutral. It didn't matter if the engine was warm or cold or if I'd been driving or not – if I was in Drive or Reverse it idled normally (just a hair over 1000rpm, smooth and quiet) but if I was in Park or Neutral it idled around 2500rpm.

The day that I noticed this happening I also discovered a coolant leak. It looks like it's probably coming out of the reservoir, as that's where the puddle was, but what's odd is that the coolant level in the reservoir wasn't actually low. I added some more coolant anyway, directly into the radiator (which may have been one mistake) and I've been keeping an eye on things but I haven't noticed any more leakage which also has me a bit confused.

I also discovered that I was low on transmission fluid! I checked it properly – drove the car around for a while until the engine was good and warm, parked it on a level surface, and then checked the dipstick with the engine running. Definitely low (although pink and clear) so I added some Dexron III (couldn't find Dexron II) and checked it again after another short drive to give the new fluid a chance to work its way into the system. It was still a bit low so I added some more and might have (another mistake) overfilled it. I'm going to drain off the excess with a siphon, but I haven't yet. This seemed to reduce the high idle problem but it hasn't actually solved it – it's still high in Park or Neutral, but not quite as high. Maybe around 2000rpm. I've been watching for leaks and haven't found any, but I'm still watching and checking the fluid level daily.

I don't like driving the truck like this, but yesterday I had to take it out on the highway and I noticed a further problem. The truck will no longer shift up into overdrive at higher speeds. I've tried turning overdrive on and off, turning ECT on and off, slowing down, stopping, turning the whole car on and off. Sometimes it will kick up into overdrive for a little while when I first start out but then will drop back down into 3rd gear after a few minutes.

Also, the temperature sensor definitely isn't working right. I don't know if it's actually gone bad of if maybe I got air into the coolant system or something when I was adding antifreeze, but the needle barely comes up off the bottom stop. Previously it would hang out just under halfway up the gauge. I think this probably has something to do with the overdrive problem as I've heard from reading threads here that the transmission won't shift into overdrive if it thinks the engine is cold. I'm planning a coolant flush (which the truck needs soon anyway) but I have no idea if this is likely to fix anything.

So that's where I'm at. High idle in Park and Neutral, no overdrive, possible coolant leak, possible air in the coolant system, possible bad thermostat, possible excess transmission fluid. Where the heck do I go from here? I'm happy to try to sort this out myself if I have instructions telling me what to do, but if this is a job for a professional instead of an idiot like me then I would still like to be able to give the mechanic a coherent story so that he'll know where to start.

Thanks a lot for the advice, I appreciate it. You guys are great.